The proposed experiments are designed to study the development of binaural perception in young infants and to clarify the effects of this development on the emerging cognitive abilities of these infants. Previous research has established that infants normally acquire the ability to turn toward a sound sometime between the fourth and fifth month of life. There are a couple of possible explanations for the emergence of sound localization at this time. It could be that binaural abilities develop at this time or binaural abilities might have been present for some time, but prior to the fourth or fifth month the infant might not have the ability to learn the association between the auditory and visual stimuli. Three experiments are proposed, with each experiment testing for a different binaural ability. Forty infants will be tested in each experiment. An equal number of three and five month olds will be tested. The experiments will consist of 12 classical conditioning trials in which a change in a binaural cue will precede a moving visual display by 8 seconds. On trials 8 and 12 the visual stimulus will be omitted to test for conditioning. The first two experiments will test for detection of interaural delay and interaural intensity differences. The third experiment will test for binaural release from masking. These experiments should determine if the onset of sound localization is accompanied either by the development of binaural hearing or the development of the ability to associate the visual and auditory cues.